MAJORANA Parity Readout Tuning Protocol

Abstract

Examples are disclosed that relate to tuning a topological qubit device. One example provides, on a quantum computing device, a method of tuning a topological qubit device into a Majorana Parity Readout (MPR) configuration. The method comprises performing optimization of an MPR signal by iteratively adjusting one or more tuning parameters of a plurality of tuning parameters, the plurality of tuning parameters comprising a quantum dot (QD) detuning, an enclosed flux, a voltage of a topological wire, a QD-Majorana zero mode (MZM) coupling, and a QD-QD coupling. Performing optimization of the MPR signal further comprises iteratively measuring the MPR signal using a readout resonator. Optimization of the MPR signal is iteratively performed until reaching a success metric.

1 . On a quantum computing device, a method of tuning a topological qubit device into a Majorana Parity Readout (MPR) configuration, the method comprising:
 performing optimization of an MPR signal by iteratively
 adjusting one or more tuning parameters of a plurality of tuning parameters, the plurality of tuning parameters comprising a quantum dot (QD) detuning, an enclosed flux, a voltage of a topological wire, a QD-Majorana zero mode (MZM) coupling, and a QD-QD coupling, and 
 measuring the MPR signal using a readout resonator, 
   
       until reaching a success metric. 
     
     
         2 . The method of  claim 1 , further comprising, prior to performing optimization of the MPR signal, tuning coupling between quantum dots and MZMs. 
     
     
         3 . The method of  claim 2 , wherein tuning coupling between quantum dots and MZMs comprises measuring a coupling between quantum dots and the MZMs by dispersive gate sensing. 
     
     
         4 . The method of  claim 2 , further comprising, prior to tuning coupling between quantum dots and MZMs,
 performing quantum dot coarse tuning,   tuning topological segments of a superconducting part of the topological qubit device into a topological phase, and   performing quantum dot fine tuning.   
     
     
         5 . The method of  claim 4 , wherein performing quantum dot fine tuning comprises pairwise tuning adjacent quantum dot pairs of a set of two or more quantum dots. 
     
     
         6 . The method of  claim 4 , wherein performing quantum dot fine tuning comprises tuning coupling between quantum dots by identifying charge transitions on each quantum dot associated with the coupling between quantum dots. 
     
     
         7 . The method of  claim 1 , wherein optimizing the MPR signal comprises selecting a quantum dot detuning to maximize a difference between parity states (ΔC Q (Φ)=|C Q (+, Φ)−C Q (−, Φ). 
     
     
         8 . The method of  claim 1 , wherein the method is performed on an interference loop comprising two or more quantum dots and two MZMs. 
     
     
         9 . The method of  claim 1 , further comprising using a readout resonator capacitively coupled to a quantum dot to probe a parity of MZMs of the quantum computing device. 
     
     
         10 . The method of  claim 1 , wherein the success metric comprises one or more of reaching a threshold value of C Q  or reaching a threshold value of ΔC Q . 
     
     
         11 . A quantum computing device, comprising:
 a topological qubit device, comprising
 a semiconducting part comprising a set of quantum dots; 
 a superconducting part comprising a plurality of topological segments configured to instantiate one or more pairs of Majorana zero modes (MZMs); and 
   a controller configured to
 adjust one or more tuning parameters of a plurality of tuning parameters, the plurality of tuning parameters comprising a quantum dot (QD) detuning, an enclosed flux, a voltage of a topological wire, a QD-MZM coupling, and a QD-QD coupling, and 
 perform optimization of a Majorana Parity Readout (MPR) signal by iteratively
 adjusting the one or more tuning parameters, and 
 measuring the MPR signal, 
 
 until reaching a success metric. 
   
     
     
         12 . The quantum computing device of  claim 11 , wherein the controller is configured to tune coupling between quantum dots and MZMs by using dispersive gate sensing to measure a coupling between quantum dots and the MZMs. 
     
     
         13 . The quantum computing device of  claim 11 , wherein the controller is configured to optimize the MPR signal comprises by selecting a quantum dot detuning to maximize a difference between parity states (ΔC Q (Φ)=|C Q (+, Φ)−C Q (−, Φ)|), and wherein the success metric comprises one or more of reaching a threshold value of C Q  or reaching a threshold value of ΔC Q . 
     
     
         14 . The quantum computing device of  claim 11 , wherein the topological qubit device comprises an interference loop comprising two or more quantum dots and two MZMs, and the controller is configured to tune coupling between the two or more quantum dots and the two MZMs of the interference loop. 
     
     
         15 . The quantum computing device of  claim 14 , further comprising a readout resonator capacitively coupled to a quantum dot of the interference loop, and wherein the controller is configured to use the readout resonator to probe a parity of the two MZMs of the interference loop. 
     
     
         16 . A quantum computing device, comprising:
 a topological qubit device, comprising
 a superconducting part comprising a plurality of topological segments configured to instantiate one or more pairs of Majorana zero modes (MZMs), 
 a semiconducting part comprising a set of quantum dots, and 
 a readout resonator coupled to a quantum dot of the set of quantum dots; and 
   a controller configured to control the quantum computing device to:
 perform quantum dot coarse tuning by tuning gates of the semiconducting part of the topological qubit device, 
 tune topological segments of the superconducting part of the topological qubit device into a topological phase, 
 perform quantum dot fine tuning, 
 tune coupling between quantum dots and MZMs, and 
 perform optimization of a Majorana Parity Readout (MPR) signal by iteratively
 adjusting one or more tuning parameters of a plurality of tuning parameters, the plurality of tuning parameters comprising a quantum dot (QD) detuning, an enclosed flux, a voltage of a topological wire, a QD-MZM coupling, and a QD-QD coupling, and 
 measuring the MPR signal using the readout resonator, until reaching a success metric. 
 
   
     
     
         17 . The quantum computing device of  claim 16 , wherein the controller is configured to control the quantum computing device to perform quantum dot fine tuning by tuning coupling between quantum dots by identifying charge transitions on each quantum dot associated with the coupling between quantum dots. 
     
     
         18 . The quantum computing device of  claim 16 , wherein the controller is configured to control the quantum computing device to perform quantum dot fine tuning by pairwise tuning adjacent quantum dot pairs of a set of two or more quantum dots. 
     
     
         19 . The quantum computing device of  claim 16 , wherein the controller is configured to control the quantum computing device to tune coupling between quantum dots and MZMs by using dispersive gate sensing to measure a coupling between quantum dots and the MZMs. 
     
     
         20 . The quantum computing device of  claim 16 , wherein the controller is configured to control the quantum computing device to optimize the MPR signal comprises by selecting a quantum dot detuning, and reaching the success metric comprises reaching a threshold value of a difference between parity states (ΔC Q (Φ)=|C Q (+, Φ)−C Q (−, Φ)|).